This application claims priority under 35 U.S.C. xc2xa7xc2xa7 119 and/or 365 to patent application Ser. No. 0003120-3 filed in Sweden on Sep. 5, 2000, the entire content of which is hereby incorporated by reference.
This invention relates to a cutting insert intended for heavy turning, which has a top side, a bottom side and a front surface interconnecting the top and bottom sides. A cutting edge is formed in the area between the top side and the front surface. The cutting edge is disposed on a comparatively thick front part of the insert, as is a chip breaker positioned behind the edge. A rear part of the insert is thinner than the front part.
In comparison with conventional turning, heavy turning is generally distinguished by the fact that in the main all parameters involved are considerably enlarged, e.g. greater cutting forces, larger chip thickness, larger and heavier workpieces, greater heat, etc. The feed during conventional turning usually is within the range of 0.05-0.8 mm/revolution, while the feed during heavy turning is within the range of 1-40 mm/revolution at the same time as the cutting depth may vary within the range of 0.2-6 mm. It is not unusual for the workpieces in question, e.g. rough shafts, to have a weight of one or more tons. Under these circumstances, it is necessary that not only the turning inserts, but also cassettes and carriers for the cutting inserts, have to be generously dimensioned.
Cutting inserts for heavy turning purposes are previously known in a plurality of different embodiments. A usual embodiment is characterized by a large thickness in relation to the depth or length of the cutting insert (i.e., the height of the front surface which extends between the cutting edge and the bottom side of the cutting insert is only slightly smaller than the length of the cutting insert, defined as the distance between the front surface and a rear end surface). Rearwards from the cutting edge, a portion of the top surface slopes obliquely downwards/rearwards, in which surface portion a straight chip breaking shoulder is formed. Said inclined surface portion ends in a delimitation surface oriented substantially parallel to the front surface. The delimitation surface at the bottom thereof transforms into a surface inclined rearwards/upwards on a short rear end portion if the insert in which a central, rearwardly porting opening is formed for a pin which has the purpose of fixing the cutting insert with the aim of counteracting lateral movements of the cutting insert. A clamping unit may be pressed against a surface inclined rearwards/upwards on the rear end portion of the cutting insert. By means of the clamping unit the cutting insert is kept clamped with the rear end surface thereof in contact with an abutment surface in the cassette (in which the cutting insert can be assembled), at the same time that the bottom side of the cutting insert is kept pressed against a bottom surface in the cassette.
However, a disadvantage of this known cutting insert for heavy turning is that in practice it is suitable for grooving operations, but not for longitudinal turning, inasmuch as the lateral stability of the cutting insert is mediocre. Thus, disturbances of the cutting insert longitudinally are only counteracted by the above-mentioned pin, which for technical, dimensioning reasons is comparatively weak.
Another disadvantage of the cutting insert is that it requires extensive and expensive grinding. Thus, the portion of the top surface sloping obliquely downwards from the cutting edge, as well as the front surface and the bottom side must be precision-ground in a plurality of steps.
An additional disadvantage is that the clamping unit for the cutting insert is exposed to considerable stresses caused by the arrival of hot chips since the top surface of the cutting insert slopes obliquely downwards/rearwards against the clamping unit. Furthermore, the known cutting insert has a limited ability to reduce the width of the chip after separation of the same from the workpiece by the cutting edge. This is something that makes it more difficult for the chip to release from the groove which is being cut.
The present invention aims at obviating the above-mentioned inconveniences of the previously known cutting insert for heavy turning and at providing an improved cutting insert for heavy turning purposes. Therefore, a primary aim of the invention is to provide a cutting insert for heavy turning, which may be secured in a stable and reliable way, and thereby not only be used for plunge-cut operations, but also for longitudinal turning during which the cutting insert is exposed to considerable lateral forces. An additional aim is to create a cutting insert for heavy turning, which is suitable for manufacture by direct pressing, e.g. of cemented carbide powder, while minimizing the number of grinding operations. Yet another aim of the invention is to create a cutting insert for heavy turning having good chip breaking properties with the purpose of improving the protection of the clamping unit against the destructive effect of the hot chip and thereby increase the service life of the clamping unit. In a particular aspect, the invention also aims at providing a cutting insert for heavy turning which quickly and effectively reduces the width of the separated chip with the purpose of facilitating chip transport.
According to the invention, at least the primary aim is attained by a heavy-turning cutting insert comprising a top side and a bottom side. The insert defines front and rear parts. The front part terminates forwardly in a front surface situated between the top and bottom sides. A cutting edge is formed in an area between the front surface and the top side. The front part includes a chip breaker disposed in the top side behind the cutting edge. The rear part is thinner than the front part as measured in a direction from the top side to the bottom side. The rear part includes two side surfaces converging rearwardly at an acute angle. The rear part includes a recess formed in the top surface and adapted for receiving a clamp.